This invention relates to a method and product aspects of spin forming an end portion of a cylindrical sheet metal workpiece to form a radial flange section and a bead or double-thickness at the periphery of the radial flange section.
At least as early as the 1980""s Spiral Fittings, Inc., presently located in Andrews, South Carolina, began spin forming cylindrical workpieces to make connector rings for cylindrical HVAC ducting. The Spiral Fittings"" connector ring is formed by spin forming a cylindrical workpiece to provide a radial flange at one of its ends. The radial flange becomes what is known as a xe2x80x9cmating flangexe2x80x9d and the unworked portion of the workpiece becomes what is known as an xe2x80x9cinsertion flange.xe2x80x9d This structure is used as a connector ring at one end of a section of HVAC ducting. The insertion flanges of two such connector rings are inserted into end portions of two sections of ducting that are to be connected together. Sheet metal screws or the like are used to connect the end portions of the sections of ducting to the insertion flanges of two connector rings. Then, the two sections of ducting are put into axial alignment with their mating flanges moved almost together. An annular seal is placed between the two mating flanges and nuts and bolts are used to connect the mating flanges together with the sealing ring held between them. A disadvantage of the Spiral Fittings"" connector ring is that the mating flanges are relatively flexible and have sharp edges at their outer peripheries.
It is known to provide connector rings for oval ducts with mating flanges having outer peripheries that are in various ways made to be blunt instead of sharp. Example connector member profiles are disclosed by U.S. Pat. No. 5,129,690, granted Jul. 14, 1992 to Manfred Meinig, Peter J. Arnoldt and Fredrick J. Arnoldt. The SMACNA HVAC Duct Construction Standards include several types of standard connector profiles for HVAC ducting. One of these profiles is the T-23 profile which has a double-thick radial flange. Another standard profile is the T-24 profile. It has a cylindrical return hem section at the periphery of the radial flange.
U.S. Pat. No. 5,983,496 granted Nov. 16, 1999 to Jeffrey Allen Hermanson discloses spin forming a cylindrical sheet metal workpiece to make a connector ring for HVAC ducting. Like Spiral Fittings, Inc., Hermanson spin forms a cylindrical workpiece to form a radial flange at one end of the workpiece. The unaltered portion of the workpiece becomes an insertion flange and the radial flange becomes a mating flange. Whereas Spiral Fittings, Inc. leaves a sharp edge at the periphery of its mating flange, Hermanson continues the spin forming operation to form a cylindrical return hem section at the periphery of the mating flange and give the connector ring a standard SMACNA T24 profile. The method of the present invention also continues the spin forming process but uses different action steps and tooling to form either a xe2x80x9cbeadxe2x80x9d, or a modified T-23 profile, at the periphery of the mating flange in place of Hermanson""s cylindrical, T-24 return hem section.
The invention includes an improved method of spin forming a cylindrical sheet metal workpiece, to form a sheet metal connector ring or sheet metal ducting. A mandrel is used that has an open center, a generally radial forming surface surrounding the open center, and an outer diameter. A first end portion of the workpiece is positioned in the open center of the mandrel and is secured to the mandrel. A second end portion of the workpiece projects axially outwardly from the center opening in the mandrel and has an outer end part. The mandrel and the workpiece are spun together about a common spin axis and the second end portion of the workpiece is progressively stretched in diameter and moved radially outwardly along the generally radial forming surface of the mandrel by a first forming tool. The mandrel and workpiece are rotated and a first forming tool is used to stretch the second end portion of the workpiece and move it radially outwardly on the radial forming surface. This is done at least until the outer end part of the second end portion of the workpiece becomes spaced generally axially from the radial forming surface substantially at the outer diameter of the mandrel. Accordingly to one aspect of the invention, the rotation of the mandrel and workpiece is continued and a second forming tool is moved against the outer end part of the second end portion of the workpiece. This second forming tool is used to curl the outer end part radially inwardly and move it substantially against an adjoining radial part of the second end portion of the workpiece that is in contact with the radial forming surface on the mandrel. Following these forming steps, the formed workpiece is removed from the mandrel to become a connector ring that has a radial flange at a first end and a cylindrical flange at a second end, wherein the radial flange has an outer marginal portion with a rounded outer edge.
Preferably, the second forming tool is used to press the outer end part of the second end portion of the workpiece flat against the adjoining radial part of the second end portion of the workpiece.
The method includes providing a first forming tool that includes a roller having a center axis. The roller is mounted for free rotation about the center axis. The roller is also provided with a convex face. The roller is positioned inside the second end portion of the workpiece, with its convex face directed towards the second end portion of the workpiece. The roller is then moved along a path that is within a plane that includes the spin axis of the mandrel and the center axis of the roller. As it moves, the roller progressively stretches the second end portion of the workpiece and progressively forces it against the generally radial forming surface of the mandrel.
The invention further includes providing a support arm for the first forming tool. The support arm is pivotally connected at a lower end to a support, for pivotal movement about a pivot axis that extends perpendicular to the center axis of the roller. The roller is mounted onto the support arm at a location spaced from the pivot axis. The support arm is swung about the pivot axis to place the roller inside of the second end portion of the workpiece, in position to contact the second end portion of the workpiece and stretch it and force it against the radial forming surface of the mandrel as the roller is being moved.
In preferred form, the mandrel is mounted to rotate about a spin axis that extends substantially vertically. As a result, the generally radial forming surface is in a plane that extends substantially horizontally.
The invention includes mounting the first forming roller for movement towards and away from the generally radial forming surface of the mandrel, and spring biasing the roller towards the radial forming surface. As a result, when the first forming roller is moved to stretch the second end portion of the workpiece and force it against the generally radial forming surface of the mandrel, the first forming roller will be urged by its contact with the workpiece and cause to move upwardly against its bias so as to provide space between its periphery and the radial forming surface of the mandrel for the workpiece material that is being moved radially outwardly in contact with the radial forming surface of the mandrel.
The present invention also includes providing a second forming tool that includes a roller that has a center axis and a cam surface that surrounds the center axis. The second forming tool is moved radially to place its cam surface against the outer part of the second end portion of the workpiece. It is further moved to cause the cam surface to cam the outer part of the second end portion of the workpiece both radially inwardly and axially towards an adjoining radial part of the second end portion of the workpiece that is in contact with the radial forming surface on the mandrel.
According to the present invention, a roller tool and a spin die or mandrel are used to spin form an end portion of a cylindrical workpiece and create a radial flange section that includes an annular groove in metal that is radially outwardly of the spin die. According to an aspect the present invention, the rotary tool is then set into and held in this groove to become a mandrel for the next step of the method. While the roller tool is held in position, a lip-forming tool is moved against the outer periphery of the workpiece. It functions to curl the workpiece upwardly to form a lip outwardly of the groove. Then the roller tool and the lip-forming tool are removed. Next, while the workpiece is still spinning, a lip-curling tool is moved radially inwardly against the lip, to curl the lip inwardly and complete formation of the bead.
The present invention includes providing a connector ring having a cylindrical insertion flange sized to be received within an end portion of a section of sheet metal ducting. It also includes a radial mating flange extending radially outwardly from one end of the insertion flange to an outer edge. The mating flange has an annular, single-thickness, inner portion and an annular, double-thickness, outer portion. The double-thickness outer portion has a laterally rounded outer edge and an inner edge that is spaced radially inwardly from the outer edge on the side of the mating flange that is opposite the insertion flange. The inner edge forms an inner boundary for the double-thickness, outer portion of the mating flange.
The present invention further includes providing a connection between adjoining ends of two duct sections. Two sheet metal connector rings of the type described are provided, one for each duct section. The cylindrical insertion flange of each connector ring is telescopically received in the end portion of its section of sheet metal ducting. The radial mating flanges of the two connector rings confront each other with their double-thickness outer portions substantially touching each other. A space is formed axially between the single thickness inner portions of the two connector rings and radially inwardly of the inner edges of the double-thickness of the outer portion of the mating flanges. A seal ring is situated in the space, contacting the inner portions of the mating flanges. Fasteners (e.g. sheet metal screws) connect the end portions of the duct sections to the insertion flanges of the connector rings. Fasteners (e.g. sheet metal screws) connect the mating flanges of the two connector rings together.